JP2002201382A - Zinc oxide microparticle for ultraviolet screening - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide zinc oxide microparticles excellent in dispersibility and ultraviolet screening effect. SOLUTION: The zinc oxide microparticles for ultraviolet screening excellent in dispersibility has the following characteristics: the average primary particle size calculated based on specific surface area is <=0.03 μm, 0.1-20 mass%, based on zinc oxide, of at least one kind of Al or Si oxide or hydroxide is also contained inside the microparticles, and the bulk density is <=0.25 g/ml.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to zinc oxide fine particles for ultraviolet shielding excellent in dispersibility, and more particularly to zinc oxide fine particles having remarkably improved dispersibility.

[0002]

2. Description of the Related Art Zinc oxide has been known as a material for shielding ultraviolet rays. However, in recent years, environmental problems such as an ozone hole expansion and an ultraviolet ray trouble caused by destruction of the ozone layer have been widely taken up by media and the like. The unexpected adverse effects of ultraviolet rays on the human body become apparent, and it is expected as one of the most representative materials for protecting the human body from harmful ultraviolet rays, and intensive research has been conducted,
In addition, it is used for a wide range of applications. In order to cope with such adverse effects on the human body (skin), sunscreen cosmetics containing zinc oxide as an ultraviolet shielding agent have attracted attention.

[0003] As described above, as the use of zinc oxide particles in cosmetics has increased in recent years, not only has the function of shielding harmful ultraviolet rays excellent, but at the same time, the compounded particles cover the skin of women. In order not to hinder the action of the natural cosmetic finish of cosmetics, which is a beauty product, it has been strongly desired that the material be as transparent as possible to visible light. Therefore, for that purpose, it is essential to make zinc oxide finer and to make it substantially transparent to visible light.

[0004] However, the zinc oxide-based ultraviolet shielding agent, which is an inorganic compound, absorbs and scatters even near-ultraviolet rays, and thus has an advantage of shielding ultraviolet rays over a wide area including near-ultraviolet rays. Since zinc oxide is an inorganic compound, it does not easily cause allergy to the skin, and can be incorporated in a large amount in cosmetics. Therefore, it is especially effective in sunscreen cosmetics when it is blended.

[0005] Zinc oxide has a particle size of 0.03.
If adjusted to ultra-fine particles of μm or less, the wavelength becomes much smaller than the wavelength of visible light, so that theoretically, visible light is hardly absorbed, so that the transparency of cosmetics is not hindered at all.

[0006] The zinc oxide finely divided as described above is a conventional ultraviolet shielding material, that is, an organic ultraviolet absorbing material, in view of the area of the ultraviolet shielding region, transparency, safety to skin, and durability of the ultraviolet shielding effect. Agent and titanium oxide,
It may be said that it has more excellent characteristics.

[0007]

However, even in the case of finely divided zinc oxide having such excellent characteristics, when it is used as an ultraviolet ray shielding agent, it has the following problems. Found them.

[0008] That is, zinc oxide particles originally have a strong cohesive force, but when they are made into fine particles as described above, the specific surface area is large, so that the cohesive force is extremely large. When such zinc oxide fine particles are blended in cosmetics or the like, they are usually used by being mixed with other organic bases. As described above, zinc oxide fine particles have strong cohesive force and are themselves. Due to aggregation, the particles are not sufficiently dispersed in the organic base. That is, the agglomerated zinc oxide particles may impair the original transparency of the cosmetic.

In addition, when such finely divided zinc oxide is incorporated into cosmetics, they are strongly agglomerated, so that the subtle smoothness inherent in the cosmetics is reduced, and the touch (feel) is deteriorated. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide good transparency, a high ultraviolet shielding effect, good storage stability, and sufficient smoothness. An object of the present invention is to provide zinc oxide suitable for obtaining a cosmetic or the like having the same.

[0011]

According to the present invention, the average primary particle diameter calculated from the specific surface area is 0.03.
zinc oxide fine particles having a particle size of not more than 0.1 μm, wherein one or two or more oxides or hydroxides of Al or Si are contained in the particles in a mass ratio of 0.1 to 2 with respect to zinc oxide.
The present invention provides zinc oxide fine particles for ultraviolet shielding excellent in dispersibility, comprising substantially 1 to 20% and having a bulk density of 0.25 g / ml or less.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The zinc oxide fine particles of the present invention are fine particles having an average primary particle diameter calculated from the specific surface area of not more than 0.03 μm.

Here, the average primary particle diameter calculated from the specific surface area is a value obtained by measuring the specific surface area by the so-called BET method and calculating the obtained value by the following equation (1). d = 1.06 / S (1) [where d: average primary particle diameter (unit: μm), S: specific surface area (unit: m ² / g)]

The average primary particle diameter of the zinc oxide particles is 0.03.
If it exceeds μm, the transparency of visible light is basically impaired, which is not preferable.

[0015] The zinc oxide particles in the present invention are finely divided as described above, and the inside of the particles further contains an oxide or hydroxide of Al or Si.
One or two kinds are used in a mass ratio of 0.1 to
It is characterized by having 20%.

In the present invention, an oxide or hydroxide of Al or Si (hereinafter sometimes referred to as an oxide of Al or the like).
Has a function of improving the dispersibility of zinc oxide particles. Therefore, it is important that these Al oxides and the like are introduced not only on the surface of the zinc oxide particles but also on the inside of the particles, and it is not sufficient to simply adhere or coat the surface of the particles. . The reason is that (i) when using zinc oxide, a shear (shearing force) is applied by a stirrer or a kneader to disperse the zinc oxide in the medium. This is because Al oxide or the like simply covering the particle surface easily peels off from the particle. (Ii) Further, when the shear is applied, the aggregated particles and the fused particles are cracked, so that a new surface is exposed, and the new particle surface has high activity and does not include Al oxide or the like. After redispersion, reagglomeration easily occurs. As described above, when only the surface of zinc oxide particles before dispersion is coated with Al oxide or the like, the dispersion effect cannot be sufficiently exhibited.

In the present invention, on the other hand, the dispersibility improving substance such as an oxide of Al is also introduced into the zinc oxide particles, so that there is no problem of peeling as described above and the particles are broken. In such a case, Al oxide or the like is present on the newly exposed surface, re-aggregation is prevented, and a stable dispersion is always obtained.

In the present invention, one or more of Al and the like are contained in the form of an oxide or a hydroxide, and the content thereof is as an oxide or a hydroxide of Al or Si. The mass ratio is 0.1 to 20%, preferably 0.1 to 10%, based on zinc oxide. If the content of Al oxide and the like is too small and less than 0.1%, the effect of improving the dispersibility cannot be sufficiently obtained, and even if the addition amount is too large and exceeds 20%, the effect is not improved. On the contrary, since the effective amount of zinc oxide decreases, the inherent ultraviolet shielding effect of zinc oxide decreases, which is not preferable. In the case where Al and Si are used in combination, this content is a value calculated as the total amount thereof.

The zinc oxide fine particles of the present invention have a bulk density of 0.25 g / ml or less. Here, the bulk density is JI
It is a value measured based on SK5101, and this value is extremely low at 0.25 g / ml or less, considering that the true density of zinc oxide (5.6) is taken into consideration. It means a very small value of only 4.4% or less. That is, when considered at the micro level, the zinc oxide fine particles of the present invention mean that the space is occupied in a very sparse state, and it can be said that the zinc oxide fine particles exist in the space in a state of being dispersed. . For this reason, the zinc oxide particles of the present invention are characterized by being in a state of being very easily dispersed.

Further, the particles of the present invention are specified by being substantially zinc oxide. The phrase “substantially zinc oxide” means that the main peak of the powder by X-ray diffraction should be that of zinc oxide. In addition to zinc oxide, impurities mixed during synthesis and impurities contained in the raw material Etc. may be included.

The zinc oxide fine particles of the present invention are extremely excellent in dispersibility, and the following measurement method is used as a method for evaluating dispersibility.

1. 1.5 g of zinc oxide of the sample was precisely weighed,
In addition to 50 g of 0% PVA / 0.2% sodium hexametaphosphate solution, a homogenizer (Nippon Seiki Seisakusho,
Ace homogenizer AM-7 type) for 10 minutes (x150
00 rpm) to obtain a dispersion of zinc oxide particles.

2. Set a 50 μm applicator on an auto applicator (manufactured by Imoto Seisakusho),
A film (thickness: 100 μm) is set. An appropriate amount of the dispersion of the zinc oxide particles is placed on the PET film, and the auto applicator is turned on to start coating. The feed speed is set on the scale 20. When the dispersion has been applied to the end of the film, the switch is turned off.

3. After the coating film is dried for one day, its thickness is measured with a micrometer. Film thickness (about 5-10μ
m), a fixed portion is cut out, and a test piece is attached to a portion of the spectroscope (manufactured by JASCO Corporation, V-570 ST type) where the incident light enters, and the transmittance is measured.

In the transmittance measured as described above, the higher the visible light transmittance and the lower the ultraviolet light transmittance, the finer the zinc oxide particles are dispersed.

The zinc oxide fine particles of the present invention have extremely good dispersibility of the particles evaluated as described above. Although the mechanism for improving the dispersibility is not completely clear at present, the present inventors presume that it will be as follows. That is, when the oxide or hydroxide of Al or Si is contained in the zinc oxide particles, the surface of the particles becomes inactive, the cohesion between the particles is reduced, and the affinity with the medium is improved. I guess.

Although the method for producing zinc oxide according to the present invention is not particularly limited, for example, the following method is employed. That is, when carbon dioxide gas is blown into a water slurry containing zinc oxide to synthesize basic zinc carbonate, water-dispersible aluminum hydroxide, aluminum oxide or water-dispersible silicon hydroxide, silicon oxide It is preferable to add a product and subject the obtained basic zinc carbonate slurry to fluidized bed drying, medium fluidized bed drying, flash drying or spray drying, and then thermally decompose to produce zinc oxide.

As the zinc oxide used as a raw material,
Any kind of so-called zinc oxide may be used,
For example, the French method of melting and evaporating zinc and oxidizing it in the gas phase, the American method of calcining, coke-reducing and oxidizing zinc ore, and precipitating basic zinc carbonate by adding soda ash to a zinc salt solution, followed by drying and firing Although it may be manufactured by any of a wet method (thermal decomposition method) or the like, it is preferable to use zinc oxide with high purity in order to obtain high-purity zinc oxide fine particles.

There is no particular limitation on the water in which the raw material zinc oxide is suspended to form a slurry, and tap water, ionic water, etc. from which impurity particles such as iron rust are removed in accordance with the required purity of the product zinc oxide. Either exchanged pure water or distilled water may be used. The carbon dioxide gas to be introduced may be used as it is as a pure gas, but in some cases, it may be used after being diluted to an appropriate concentration with a diluent gas such as air or nitrogen.

The apparatus for carrying out the basic zinc carbonate formation reaction is not particularly limited, but includes, for example, a stirring means, a heating means, a gas introduction / dispersion means, and an introduction means for Al oxide and the like. The zinc oxide particles are suspended without being precipitated and kept in a slurry state, and a carbon dioxide gas and an Al oxide are introduced into the slurry, and the zinc oxide particles and the carbon dioxide are mixed in the presence of the Al oxide particles. It is preferable to use a stirred tank type reactor in which the reaction can be performed by sufficiently contacting with carbon gas.

The slurry concentration of the raw material zinc oxide is at least 0.1 to 20% by mass, preferably 0.1 to 10% by mass.
It is desirable to have a relatively low concentration of 1% by mass, more preferably 1% to 5% by mass. When the slurry concentration exceeds this range, basic zinc carbonate having a large particle diameter is generated or aggregated particles are easily generated, and it is difficult to obtain fine particles having the desired dispersibility in the present invention. On the other hand, if the slurry concentration is much lower than this, the amount of water to be removed in the subsequent drying step or the like becomes excessively large, which lowers production efficiency and is not preferable in terms of energy.

As a method for introducing the carbon dioxide gas, any method can be used as long as the slurry and the gas can come into effective contact, and the method is not particularly limited. For example, a perforated plate or a diffuser tube may be provided at the bottom of the reaction tank. A gas disperser (sparger) is installed, and carbon dioxide gas is blown into the liquid through the sparger. More preferably, the gas is subdivided by a stirring blade, and the carbon dioxide gas is dispersed as a group of fine bubbles throughout the slurry. A method in which a closed vessel is used as a reaction vessel, a pressurized carbon dioxide gas is introduced, and a gas is absorbed from the free surface of the upper part of the slurry can be adopted. In the latter case, it is more preferable to form a vortex by stirring and forcibly renew the surface of the slurry liquid to promote gas absorption.

When basic carbonic acid is formed by blowing carbon dioxide, one or two of oxides or hydroxides of Al or Si are added to the zinc oxide in a mass ratio of 0.1 to The raw material of the oxide or hydroxide is added so as to have a content of 20%, preferably 0.1 to 10%, and is contained in the basic zinc carbonate. Particularly preferred examples of the raw material include fine particle sols such as colloidal silica and colloidal alumina, which are introduced into the reaction solution by an introduction means such as a dropping device. In addition,
Any compound that generates oxides or hydroxides of Al and Si by blowing carbon dioxide gas may be used. It is preferable that these colloidal silicas and the like are introduced almost continuously by means such as dropping in accordance with the supply speed of the carbon dioxide gas. Thus, fine sol particles such as oxides of Al are always present in the vicinity where the particles of basic zinc carbonate are generated and grown.
It is considered that fine particles such as oxides of Al are taken in, and thus the oxides of Al and the like are present inside the basic zinc carbonate particles thus formed.

As the stirring means, any of ordinary stirrers, for example, paddle-type stirrers, propeller-type stirrers, turbine-type stirrers and the like are suitably used.

The basic zinc carbonate forming reaction of the present invention can be carried out by various methods in practice. For example, first, a zinc oxide slurry is charged into a reaction tank, and carbon dioxide gas is continuously added to the slurry. Semi-continuous method (semi-batch method) in which the basic zinc carbonate slurry is produced by supplying the zinc oxide slurry and the carbon dioxide gas to the reaction vessel continuously to produce the basic zinc carbonate slurry. A method such as a continuous method in which the generated basic zinc carbonate slurry is continuously overflowed from the reaction tank and withdrawn is preferably employed.

The reaction temperature for the basic zinc carbonate forming reaction is not particularly limited, but is 10 to 80 ° C., preferably 20 to 60 ° C. Although the reaction itself proceeds at a higher speed as the temperature is higher, the solubility of carbon dioxide gas in water decreases as the temperature increases, and the gas concentration in the liquid decreases. Therefore, whether the reaction temperature is lower or higher than the above-mentioned temperature range, the overall reaction rate is undesirably slow. The reaction time (in the case of the continuous method, the average residence time in the reaction vessel) can vary depending on the reaction temperature, the concentration of carbon dioxide introduced, and the like, but is usually about 10 minutes to 10 hours, preferably about 30 minutes to 5 hours. It is. In order to maintain the temperature, it is preferable that the reactor is provided with a heating means, a heat keeping means and a temperature control means.

In the present invention, the slurry containing the basic zinc carbonate obtained by the above-described basic zinc carbonate formation reaction is dried by fluidized bed drying, medium fluidized bed drying, flash drying, spray drying, or the like to remove water. Remove to dry powder.

In this case, since the slurry concentration of the slurry containing the basic zinc carbonate is considerably low, it is not desirable to dry the slurry as it is in terms of heat energy economy. Therefore,
Preferably, it is desirable to concentrate the slurry in advance, especially by mechanical means.

The degree of concentration of the slurry is not particularly limited as long as the concentrated slurry retains fluidity and is supplied and treated after being atomized into a fluidized bed dryer or the like. It is preferably from 20 to 50% by mass, preferably from 20 to 45% by mass, more preferably from 25 to 40% by mass from the viewpoint of handling and economy.

The mechanical means for concentration is not particularly limited, but is preferably a precipitation concentration using a thickener, a centrifugal sedimentation using a centrifugal sedimenter, a centrifugal classification using a liquid cyclone, or the like. An optimal device can be adopted according to the concentration, the processing amount, and the like.

In the present invention, the basic zinc carbonate slurry is preferably concentrated in advance, as described above, and is then supplied to a drying apparatus such as a fluidized bed dryer, a medium fluidized bed dryer, a flash dryer or a spray dryer. Provided and dried. The supplied slurry becomes droplets containing fine particles in such a drying device, and this forms a fluidized bed with hot air for drying.
Drying while floating (fluidized bed drying, fluidized bed medium drying) or drying in a very short time while being carried by hot air (flash drying or spray drying) gives a dry powder of basic zinc carbonate.

As the drying device, a spray dryer is particularly preferred in that the most dispersed basic zinc carbonate fine particles can be obtained. When a spray dryer is used, a rotating disk, a two-fluid nozzle, a pressurizing nozzle, or the like can be appropriately used as a sprayer, and the temperature of hot air for drying is 200 to 300 at the inlet.
C., preferably at about 100 to 150 C. at the outlet.

Finally, the dried basic zinc carbonate is thermally decomposed (calcined) to obtain zinc oxide. The heat decomposition temperature is a temperature at which basic zinc carbonate is decomposed into finely divided zinc oxide having good dispersibility, and is 200 to 1000 ° C, preferably 200 to 1000 ° C.
A temperature of 500 ° C, more preferably 250-350 ° C, is desirable. If the temperature is too low, the decomposition will be insufficient, and if the temperature is too high, the particles will grow too much due to aggregation or sintering, and both are unfavorable because the dispersibility deteriorates. The thermal decomposition time may vary depending on the treatment amount, heating temperature, type of heating furnace, etc.
The time is from about minutes to 20 hours, preferably about 1 to 10 hours.

The thermal decomposition is performed in an oxidizing atmosphere such as air.
This is performed in a furnace capable of heating the basic zinc carbonate particles to the above-mentioned temperature. The heating furnace is not particularly limited,
For example, a box furnace, a rotary furnace (rotary kiln), a moving bed furnace, a fluidized bed furnace, an electric furnace, a gas heating furnace, an infrared heating furnace, and the like are preferably used.

The heat-decomposed zinc oxide fine particles have excellent dispersibility and can be used as they are for ultraviolet shielding of cosmetics and the like of the present invention. In addition, if desired, a ball mill, a rod mill, an attrition mill, a jet mill,
It can be used after being further pulverized by a fine pulverizer such as a micron mill. These pulverizers are appropriately selected according to the cosmetics and the like to be blended and the paint.

[0046]

The present invention will be described below with reference to examples. However, these are merely examples of the embodiments, and the technical scope of the present invention is not limited by these.

Example 1 (1) JIS K1410 1 obtained by French method
A 62.5 g / L zinc oxide slurry was prepared using seed zinc oxide and ion-exchanged water. 5.6 L of this slurry was charged into a reaction vessel equipped with an air diffuser at the bottom having an internal volume of 10 L and equipped with a stirrer, a slurry supply means and a heat retaining mechanism, and kept at a temperature of 30 ° C. with stirring at 5 L / min. Injected carbon dioxide gas. While blowing this gas, 1.4 L of a colloidal silica solution (concentration: 12.5 g-SiO _{2 /} L) was continuously supplied dropwise over 2 hours. After 2 hours, the blowing was terminated, and the product was analyzed by XRD to confirm that basic zinc carbonate had been formed.

(2) After allowing this slurry to stand for 2 hours,
The supernatant was discarded to obtain a basic zinc carbonate slurry having a slurry concentration of 20%. The supernatant was analyzed to confirm that there was no silica content. That is, it was confirmed that all the supplied silica was introduced into the basic zinc carbonate. This slurry was fed to a spray dryer adjusted to an inlet gas temperature of 250 ° C. and an outlet gas temperature of 130 ° C. to obtain basic zinc carbonate particles. The particle size of the particles was about 100 μm.

(3) The particles were placed in a box furnace heated to 250 ° C. and thermally decomposed for 5 hours to obtain zinc oxide fine particles.

The specific surface area of the obtained zinc oxide was measured by the BET method, and a value of 50 m ² / g was obtained. The particle size calculated from this specific surface area is 0.02 μm. Further, the silica content in the zinc oxide was analyzed, and it was confirmed that the zinc oxide contained 4.8% of the silica content. The bulk density measured based on JIS K5101 was 0.20 g / ml.

Next, in order to evaluate the dispersibility of the obtained zinc oxide fine particles, the above-described dispersibility evaluation test was performed.
The transmittance was measured. Table 1 shows the results. As is clear from the table, it can be seen that the zinc oxide of the present invention has high visible light transmittance and ultraviolet shielding ability, and is excellent in dispersibility.

Comparative Example 1 (1) A 50 g / L zinc oxide slurry was prepared using JIS K1401 zinc oxide obtained by the French method and ion-exchanged water. 7 L of this slurry was charged into a reaction vessel equipped with a stirrer having an internal volume of 10 L and a diffuser tube at the bottom, and carbon dioxide gas was blown at 5 L / min with stirring. After 2 hours, blowing was stopped, and the product was subjected to XRD analysis to confirm that basic zinc carbonate had been formed.

(2) After allowing this slurry to stand for 2 hours,
The supernatant was removed to obtain a basic zinc carbonate slurry having a slurry concentration of 20%. This slurry is heated at an inlet gas temperature of 250 ° C.
The mixture was fed to a spray dryer adjusted to an outlet gas temperature of 130 ° C. to obtain basic zinc carbonate particles. The particle size of the particles was about 110 μm.

(3) The particles were placed in a box furnace heated to 250 ° C. and thermally decomposed for 5 hours to obtain zinc oxide fine particles.

The specific surface area of the obtained zinc oxide was measured by the BET method to obtain a value of 47 m ² / g. The particle size calculated from this specific surface area is 0.02 μm. JIS K
The bulk density measured based on 5101 is 0.30 g / ml
Met. Next, in order to measure the dispersibility of the obtained zinc oxide fine particles, the above-described dispersibility evaluation test was performed, and the transmittance was measured. The results are shown in Table 1 below. As is clear from the table, the zinc oxide manufactured using the conventional method does not contain oxides of Al and Si, etc., and has a high bulk light density, and thus has a higher visible light transmittance than that of Example 1. It can be seen that the ultraviolet shielding ability is low and the dispersibility is poor.

(Comparative Example 2) The zinc oxide obtained in Comparative Example 1 was added to a calculated amount of an aqueous solution of sodium silicate at which the silica coating amount was 5% by mass, and this solution was vigorously stirred to form a slurry. Thereafter, hydrochloric acid was gradually added to lower the pH to 7, thereby depositing silicon oxide. The solution was allowed to stand overnight, filtered, washed and dried to obtain a zinc oxide powder whose surface was coated with silicon oxide. Perform a dispersibility evaluation test of this zinc oxide powder,
The transmittance was measured. The results are shown in Table 1 below. As can be seen from the table, only the surface of zinc oxide coated with silica,
It can be seen that the visible light transmittance is higher than that of Example 1, but the ultraviolet ray shielding ability is low and the dispersibility is poor.

Example 2 (1) A 50 g / L zinc oxide slurry was prepared using JIS K1410 three kinds of zinc oxide obtained by the French method, the supernatant obtained in Example 1, and pure water. This slurry was equipped with an air diffuser at the bottom of an inner volume of 10 L, a stirrer,
4. In a reaction vessel equipped with a slurry supply means and a heat retaining mechanism,
6 L, the temperature was kept at 40 ° C., and carbon dioxide gas was blown at 10 L / min with stirring. Colloidal alumina solution (concentration: 12.5 g-Al ₂ O ₃ / L) while blowing this gas
4 L were continuously supplied over 2 hours. After 2 hours, the blowing was terminated and the product was analyzed by XRD to confirm that basic zinc carbonate had been formed.

(2) After allowing this slurry to stand for 2 hours,
The supernatant was discarded to obtain a basic zinc carbonate slurry having a slurry concentration of 27%. This slurry is heated at an inlet gas temperature of 250 ° C.
The mixture was fed to a spray dryer adjusted to an outlet gas temperature of 130 ° C. to obtain basic zinc carbonate particles. The particle diameter of the particles was about 400 μm.

(3) The particles were charged into a retort furnace heated to 300 ° C. (the retort was rotated at 10 rpm) and thermally decomposed for 5 hours to obtain fine zinc oxide particles. The specific surface area of the obtained zinc oxide was measured by the BET method to be 43 m ²
/ G. The particle size calculated from this specific surface area is 0.02 μm. The alumina content in zinc oxide was analyzed, and it was confirmed that the zinc oxide contained 0.9% alumina. JI
The bulk density measured based on SK5105 is 0.3 g /
ml.

Next, in order to evaluate the dispersibility of the obtained zinc oxide fine particles, the above-mentioned dispersibility evaluation test was performed, and the transmittance was measured. The results are shown in Table 1 below. As is clear from the table, it can be seen that the zinc oxide of the present invention has high visible light transmittance and ultraviolet shielding ability, and is excellent in dispersibility.

Example 3 (1) A zinc oxide slurry of 62.5 g / L was prepared using JIS K1410 one kind zinc oxide obtained by the French method and ion-exchanged water. This slurry has an internal volume of 10 L
5.6 L was charged into a reaction vessel equipped with a stirrer, a slurry supply means and a heat retaining mechanism, and the temperature was kept at 30 ° C., and carbon dioxide gas was blown at 5 L / min with stirring. While injecting this gas, a colloidal silica solution (concentration 2
(5 g-SiO _{2 /} L) was continuously supplied over 2 hours. After 2 hours, blowing was completed and the product was analyzed by XRD to confirm that basic zinc carbonate had been formed.

(2) After allowing this slurry to stand for 2 hours,
The supernatant was discarded to obtain a basic zinc carbonate slurry having a slurry concentration of 20%. The supernatant was analyzed to confirm that there was no silica content. This slurry was fed to a spray dryer adjusted to an inlet gas temperature of 250 ° C. and an outlet gas temperature of 130 ° C. to obtain basic zinc carbonate particles. The particle size of the particles was about 100 μm.

(3) The particles were placed in a box furnace heated to 250 ° C. and thermally decomposed for 5 hours to obtain zinc oxide fine particles. The specific surface area of the obtained zinc oxide was measured by the BET method to obtain a value of 55 m ² / g. The particle size calculated from this specific surface area is 0.02 μm. Further, the silica content in the zinc oxide was analyzed, and it was confirmed that the zinc oxide contained 9% of the silica content. The bulk density measured based on JIS K5105 was 0.20 g / ml.

Next, in order to measure the dispersibility of the obtained zinc oxide fine particles, the above-described dispersibility evaluation test was performed, and the transmittance was measured. The results are shown in Table 1 below. As is clear from the table, it can be seen that the zinc oxide of the present invention has high visible light transmittance and ultraviolet shielding ability and is excellent in dispersibility.

[0065]

[Table 1]

[0066]

As is clear from the table, the zinc oxide fine particles of the present invention are high in visible light transmittance and ultraviolet ray shielding ability and excellent in dispersibility, and are excellent in dispersibility and are ultraviolet ray shielding zinc oxide fine particles. You can see that. Therefore, it is suitably used for various uses that require transparency at the same time as ultraviolet shielding such as cosmetics and paints.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tatsuhiko Ikeda 669, Yokota, Oizuka, Iizuka-shi, Fukuoka F-term (reference) 4C083 AB211 CC19 EE01 EE06 EE07 EE17 FF01 4G047 AA04 AA05 AB02 AC02 AD04 4J037 AA11 CA08 CA12 CB23 DD01 DD05 EE15 EE35 EE43 FF02 FF15

Claims (1)

[Claims] 1. A zinc oxide fine particle having an average primary particle diameter calculated from a specific surface area of not more than 0.03 μm, wherein one or more of oxides or hydroxides of Al or Si are also present inside the particle. Two or more kinds are contained in a mass ratio of 0.1 to 20% with respect to zinc oxide, and the bulk density is 0.25 g.
/ Ultraviolet ray shielding zinc oxide fine particles having excellent dispersibility, comprising substantially zinc oxide.